WO2000033496A1 - Frequency synchronizing device for ofdm/cdma system - Google Patents
Frequency synchronizing device for ofdm/cdma system Download PDFInfo
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- WO2000033496A1 WO2000033496A1 PCT/KR1999/000726 KR9900726W WO0033496A1 WO 2000033496 A1 WO2000033496 A1 WO 2000033496A1 KR 9900726 W KR9900726 W KR 9900726W WO 0033496 A1 WO0033496 A1 WO 0033496A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/02—Channels characterised by the type of signal
- H04L5/023—Multiplexing of multicarrier modulation signals
- H04L5/026—Multiplexing of multicarrier modulation signals using code division
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
- H04L27/2659—Coarse or integer frequency offset determination and synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
- H04L27/266—Fine or fractional frequency offset determination and synchronisation
Definitions
- the present invention relates generally to a modulation/demodulation device in an orthogonal frequency division multiplexing/code division multiple access (OFDM/CDMA) system, and in particular, to a device for synchronizing a frequency in a time domain in OFDM/CDMA system.
- OFDM/CDMA orthogonal frequency division multiplexing/code division multiple access
- an OFDM technique is frequently used in digital transmission systems such as a digital audio broadcasting (DAB) system, a digital television system, a wireless local area network (WLAN), and a wireless asynchronous transfer mode (WATM) system.
- DAB digital audio broadcasting
- WLAN wireless local area network
- WATM wireless asynchronous transfer mode
- the OFDM technique is a type of multi-carrier technique which modulates transmission data after dividing, and then transmits the divided modulated data in parallel.
- the OFDM technique was not widely used for the complex structure.
- various digital signal processing techniques including the fast Fourier transform (FFT) and the inverse FFT (IFFT) has made it possible to utilize the OFDM system.
- FFT fast Fourier transform
- IFFT inverse FFT
- the OFDM system may have an optimal transmission efficiency during high-speed data transmission by maintaining orthogonality between sub-carriers. Because of the optimal transmission efficiency, the OFDM/TDMA and OFDM/CDMA systems have been proposed for use with the WATM system since it requires high-speed
- FIG. 1 there is shown a block diagram of a general
- the OFDM/CDMA system includes a transmitter 100 and a receiver 120.
- the transmitter 100 and the receiver 120 may be equally applied to both the forward link and the reverse link.
- a plurality of spreaders 101 spread transmission data using orthogonal codes of length N and PN spreading sequences.
- N is 256 in the OFDM/CDMA system.
- the spreaders 101 include spreaders for user identification and spreaders for base station identification.
- the spreaders 101 include spreaders for channel spreading and spreaders for user identification.
- the N-bit data will be referred to as chip data.
- the chip data spread by the spreaders 101 is input to a summer 102 after pilot signal insertion (not shown).
- the chip data is summed in the summer 102 on a chip unit basis and is output in series to a serial/parallel converter 103.
- the serial/parallel converter 103 outputs the serial chip data provided from the summer 102 in parallel.
- the number of the parallel chip data output can be equal to N or not equal to N.
- the number of the parallel chip data is assumed to be N.
- the parallel sample data is input to an inverse fast Fourier transform (IFFT) device 104.
- the IFFT device 104 receiving N parallel data samples, performs OFDM modulation on the chip data.
- the IFFT device 104 performs IFFT on the chip data, and carries the processed chip data on different sub-carriers having orthogonality in a frequency domain.
- the sub-carriers are output in the time domain.
- the data output from the IFFT device 104 will be defined as sample data, and N data samples will be defined as an OFDM symbol.
- the parallel output sample data is input to a parallel/serial converter 105.
- the parallel/serial converter 105 outputs the same data in series. Further, the parallel/serial converter 105 inserts a guard interval on an N-sample data unit basis, i.e., one-OFDM symbol unit basis.
- the guard interval is data obtained by copying some sample data at the rear of an OFDM symbol comprised of N data samples, and is inserted at the front of the OFDM symbol.
- the data in which a guard interval is inserted on an OFDM symbol unit basis is defined as an OFDM frame.
- the length of the guard interval should be set longer than an impulse response length.
- a transmission filter 106 filters the data output from the parallel/serial converter 105 and transmits the filtered data over a radio channel 107 using an RF (Radio Frequency) module (not shown).
- the radio channel 107 is an additive white Gaussian channel, so that additive white Gaussian noises are added by an adder 109.
- the receiver 120 receives a carrier with the additive white Gaussian noises over the additive white Gaussian channel.
- the received carrier is converted to a baseband signal through an RF module (not shown).
- a multiplier 110 compensates for frequency error generated in channel 107 using a frequency correction signal received.
- An analog to digital converter 115 converts the frequency-corrected analog signal input from the multiplier 110 to digital sample data stream.
- a serial/parallel converter 111 receives the OFDM symbol in series and outputs N data samples constituting the OFDM symbol in parallel.
- the receiver 120 commonly includes a guard interval remover for removing the guard interval inserted on an OFDM frame unit basis before parallelizing the sample data stream.
- a fast Fourier transform (FTT) device 112 performs OFDM demodulation on the received sample data carried on the sub- carriers in parallel and converts the respective sub-carriers to the original chip data in the frequency domain.
- a parallel/serial converter 113 converts the parallel chip data to serial chip data.
- a despreader 114 despreads the serial chip data input from the parallel/serial converter 113 to restore the original data.
- the OFDM system is performed in two steps, namely, a coarse synchronization and a fine synchronization.
- the coarse synchronization step removes an initial frequency offset corresponding to multiples of the sub-carrier interval
- the fine synchronization step removes the residual frequency offset remaining after coarse synchronization.
- FIGS. 2 to 4 show a frequency synchronization device for the receiver, using the coarse frequency synchronization technique and the fine frequency synchronization technique.
- the technique proposed by Classen & Myer uses a test correction frequency, and calculates a correlation between known transmission data and received data while shifting the test correction frequency by a predetermined frequency interval, thereby estimating the frequency offset.
- This technique uses a property that the correlation value becomes maximum when the test correction frequency is nearest to an actual frequency offset shifted in the actual channel.
- a multiplier 128 compensates for a frequency offset of a received signal using a test correction frequency received.
- An analog/digital converter (ADC) 129 converts the received analog data to digital data.
- a guard interval remover 122 removes the guard interval from the received data.
- a guard interval removing method sets a window having a length of two OFDM symbols and one guard interval, calculates a correlation value while shifting the window by samples, and removes the guard interval beginning at a position where the maximum value starts to be output.
- An FFT device 124 performs FFT to modulate the sample data output from the multiplier 128, and outputs a chip data stream in common to the despreader, a delay 125 and an estimator 127.
- the delay 125 delays the chip data for one-chip data length time and then outputs the delayed chip data to the estimator 127.
- a reference tone pattern generator 126 generates a reference tone having a predetermined pattern known to both the mobile station and the base station, and provides the generated reference tone pattern to the estimator 127.
- the estimator 127 outputs an estimated frequency offset f e by receiving the chip data output from the FFT device 124, the delayed chip data output from the delay 125 and the reference tone pattern output from the reference tone generator 126. That is, the estimator 127 outputs the estimated frequency offset _ using a correlation value between the chip data of the two consecutive subchannels and the reference tone known to the receiver.
- the estimated frequency offset f e is a factor in determining the test correction frequency.
- the estimator 127 calculates the estimated frequency offset in accordance with Equation ( 1 ) below.
- Equation (1) where f e denotes the estimated frequency offset, Z l k and Z ]+1 k denote the chip data of the consecutive sub-carriers, X l k denotes the data stream previously known to the receiver during data reception, V denotes the frequency shift for sync estimation, '1' denotes an index of the sample data, and 'k' denotes an index of the OFDM symbol. It is noted from Equation (1) that the two consecutive chip data exist in the same OFDM symbol.
- An analog to digital converter (ADC) 131 converts analog data received from a multiplier 140 to digital sample data.
- a guard interval remover 133 removes from the received data a guard interval which is used for distinguishing the received sample data and for preventing interference between the symbols.
- An FFT device 135 performs a FFT on the sample data output from the ADC 131, and outputs a chip data stream to both a despreader and a correlator 139.
- a reference tone pattern generator 137 generates a predetermined reference tone pattern and provides correlator 139 with the reference tone pattern.
- the conelator 139 outputs an estimated frequency offset f e using the chip data output from the
- the coarse frequency synchronization technique proposed by Nogammi & Nagashima is different from the technique proposed by Classen & Myer in that a correlation value between one data sample and a reference tone known to the receiver is used for frequency synchronization instead of a correlation value between two consecutive data samples and the reference tone.
- the technique proposed by Dafara & Adami acquires fine frequency synchronization using a property of the transmission signal, namely that when there exists no frequency offset, a signal in the guard interval of the received signal is identical to the original signal.
- a signal in the guard interval and the original signal have different phases due to the frequency offset, and finally, when the signal in the guard interval is multiplied by the original signal, an imaginary part of the resulting value contains information about the frequency offset.
- the present invention removes the residual frequency offset according to this property.
- a bandpass filter 141 filters analog data and only permits a frequency band that is proper for the system to pass.
- a multiplier 143 multiplies the filtered received data by the test correction frequency in order to correct a fine frequency offset.
- An ADC 145 converts the frequency offset-corrected analog data output from multiplier 143 to digital OFDM frame data.
- a guard interval remover 153 removes the guard interval included in the OFDM frame from the OFDM frame output from the ADC 145, and outputs OFDM symbols.
- An FFT device 155 parallelizes the OFDM symbols output from the guard interval remover 153 into N data samples, and performs FFT on the N data samples to output N-chip data.
- a frequency detector 147 detects a frequency error for compensating for the fine frequency offset.
- the frequency detector 147 can detect the frequency error through either a path 'a' or a path 'b'.
- the frequency error detection through the path 'a' uses the guard interval.
- the frequency detector 147 detects the guard interval from the OFDM frame output from the ADC 145.
- the detected guard interval is compared with a sample data interval in order to detect the frequency error.
- the sample data interval was used to generate the guard interval out of pure sample data.
- Frequency error detection through the path 'b' uses the fast Fourier transformed-chip data from FFT 155.
- a carrier extractor 157 is required for frequency error detection through the path 'b'.
- the carrier extractor 157 extracts pilot chip data that is inserted in the chip data stream output from the FFT 155 and provides the frequency detector 147 with the extracted pilot chip data.
- the frequency detector 147 detects the frequency error by comparing the pilot chip data with a known signal.
- the technique proposed by Dafara & Adami uses the 'a' path wherein the frequency detector 147 uses the guard interval from the digital data output from the ADC 145 and outputs an estimated fine frequency offset calculated by 1 L
- N denotes the sample number of OFDM symbol
- I denotes the sample number in the guard interval
- the technique proposed by Moose uses the 'b' path wherein the frequency detector 147 receives the pilot signal from the FFT device 155 through the carrier extractor 157 and outputs an estimated fine frequency offset calculated by
- L denotes the sample number used when estimating the frequency error.
- the estimated fine frequency offset detected by the frequency detector 147 through path 'a' or 'b' is input to a voltage controlled oscillator (VCO) 151 through a lowpass filter 149.
- VCO voltage controlled oscillator
- the voltage controlled oscillator 151 generates the test correction frequency depending upon the estimated fine frequency offset and provides the generated test correction frequency to the multiplier 143.
- the guard interval based (GIB) fine frequency synchronizing technique through the path 'a' is implemented at a pre-FFT stage, and the pilot signal based fine frequency synchronizing technique (or maximum likelihood estimation (MLE)) through the path 'b' is implemented at a post-FFT stage.
- GOB guard interval based
- MLE maximum likelihood estimation
- the received baseband signal can be expressed as x(t)e J2 ⁇ fe ' .
- the phase difference between two samples is constantly 2 ⁇ / c t .
- the phase difference between two samples is 2 ⁇ f c t' which is affected by the length of the guard interval.
- the conventional coarse frequency synchronization technique is susceptible to channel noises, therefore, it is difficult to guarantee the system performance.
- the fine frequency synchronization is locked at a sub-carrier which is located nearest to a position of the residual frequency offset.
- the residual frequency offset has a value of about +0.5% of the sub-carrier interval, the conventional fine frequency synchronization technique cannot acquire synchronization.
- the MLE algorithm processes the data at the post-FFT stage, thereby causing a delay in acquiring synchronization. This delay will increase the time required for synchronization acquisition.
- an object of the present invention to provide a frequency synchronizing device for performing frequency synchronization using only the received input signal in a time domain in an OFDM/CDMA system.
- a frequency synchronizing device for an OFDM/CDMA communication system which exchanges data using an OFDM frame including OFDM symbols each comprised of a plurality of data samples, and a guard interval inserted at the head of each symbol to prevent interference between the symbols.
- the frequency synchronizing device comprises a frequency corrector for compensating for a frequency offset of the received analog data according to a frequency conection signal; an analog/digital converter for converting the received analog data to an
- the copy data is comprised of some data samples out of the OFDM symbols and is used to sequentially estimate coarse, regular and fine frequency offsets, and provide the frequency conector with the frequency conection signal conesponding to the estimated frequency offsets.
- FIG. 1 is a block diagram illustrating a general OFDM/CDMA system
- FIG. 2 is a block diagram illustrating a coarse frequency synchronizing device in the general OFDM/CDMA system
- FIG. 3 is a block diagram illustrating another coarse frequency synchronizing device in the general OFDM/CDMA system
- FIG. 4 is a block diagram illustrating a fine frequency synchronizing device in the general OFDM/CDMA system.
- FIG. 5 is a block diagram illustrating a frequency synchronizing device for a receiver in an OFDM/CDMA system according to an embodiment of the present invention.
- a frequency synchronizing device for an OFDM/CDMA system filters received analog data.
- a frequency conector 161 compensates for a frequency offset of the bandpass filtered data according to a first and a second frequency conection signal and a control signal.
- An ADC 162 converts the received frequency offset-compensated analog data to digital sample data, and provides the digital sample data to a guard interval remover 163.
- the guard interval remover 163 removes a guard interval which is inserted on a OFDM frame unit basis, from the sample data.
- a frequency synchronizer 200 calculates an estimated frequency offset for coarse, regular and fine frequency synchronizing depending on a signal output from the ADC 162, and outputs the first and second frequency conection signals according to the estimated frequency offsets.
- a controller 195 controls the overall operation of the frequency synchronizing device.
- the controller 195 outputs a coarse delay signal for performing initial coarse frequency synchronization, outputs a regular delay signal after acquiring coarse frequency synchronization, and outputs a fine delay signal after acquiring regular frequency synchronization.
- a delay 164 delays an OFDM frame output from the ADC 162 for a predetermined time. The delay time is identical to one- OFDM frame time.
- a guard interval/carrier extractor 166 receives the OFDM frame output from the ADC 162 and the OFDM frame output from the delay 164, and extracts therefrom copy data to create the above guard interval and a guard interval in the original OFDM symbol.
- a shift index generator 165 outputs a shift index of an integer according to the coarse delay signal output from the controller 195, and upon receipt of the regular delay signal, outputs a shift index of 1/10 unit.
- a coarse frequency synchronizer 180 is comprised of the following: a correlation value detector 167, a minimum/maximum value (MIN/MAX) detector 168, and an adder 169.
- Conelation value detector 167 receives the guard interval and the copy data from the interval/carrier extractor 166 and the shift index value from the shift index generator 165, and extracts a correlation value while shifting the guard interval and the copy data on a sample data unit basis.
- the extracted conelation value is provided to a minimum/maximum value (MIN/MAX) detector 168.
- the MIN/MAX detector 168 detects the maximum or minimum value of the correlation value input from the correlation value detector 166 according to the delay signal output from the controller 195.
- the MIN/MAX detector 168 detects the minimum value according to the coarse delay signal input from the controller 195.
- the minimum value detected at this point is a coarse estimation signal. Further, upon detection of the minimum value, the MIN/MAX detector 168 informs the controller 195 of detection of the minimum value.
- the received signal is shifted overall, so that noises are inserted in the guard interval.
- the coarse frequency offset is estimated in the guard interval/carrier extractor 166, the conelation value detector 167 and the MIN/MAX detector 168.
- the estimated frequency offset for coarse frequency synchronization by detecting guard interval power in the time domain is calculated by
- K MIN and K MAX denote the minimum and maximum sub-carrier numbers of FFT, respectively, and Zi denotes a symbol.
- the guard interval/carrier extractor 166 extracts the guard interval and copy data from an OFDM frame output from the ADC 162.
- the conelation value detector 167 receives the guard interval and copy data from the guard interval/carrier extractor 166 and a shift index having 1/10 length of the sample data from the shift index generator 165, and detects a conelation value while shifting the sample data in the detected guard interval and sample data of the copy data, which is identical to the above sample data, by 1/10 band.
- the MIN/MAX detector 168 detects a conelation value having the maximum power out of the conelation values detected by the conelation value detector 167, and outputs a regular estimated frequency offset which is a regular estimation signal.
- the estimated frequency offset for regular frequency synchronization is calculated by
- f ⁇ a denotes a compulsory test conection frequency and has a value larger than '0' but smaller than '1 '.
- the MIN/MAX detector 168 After estimation of the coarse frequency offset and the regular frequency offset, the MIN/MAX detector 168 outputs the coarse estimation signal and a regular estimation signal. An adder 169 adds the coarse estimation signal to the regular estimation signal to generate the first frequency correction signal, and provides the first frequency conection signal to the frequency conector 161.
- the guard interval/carrier extractor 166 extracts the guard interval and copy data from an OFDM frame output from the ADC 162, and provides the extracted guard interval and copy data to a frequency detector 170.
- the fine frequency synchronization is accomplished using a fine frequency synchronizer 190 and is performed after acquiring the coarse and regular frequency synchronization.
- Fine frequency synchronizer 190 is comprised of frequency detector 170, a lowpass filter 171and a voltage controlled oscillator (NCO).
- NCO voltage controlled oscillator
- the GIB frequency synchronization technique described with reference to FIG. 4 is used for the fine frequency synchronization.
- frequency detector 170 under the control of controller 195, receives the sample data in the guard interval output from the guard interval/carrier extractor 166 and sample data of the copy data, which is identical to the above sample data, to detect a phase difference between the two sample data, and determines the detected phase difference as a fine frequency offset.
- the frequency detector 170 provides the fine frequency offset to a voltage controlled oscillator (VCO) 172 via a lowpass filter 171.
- VCO voltage controlled oscillator
- the voltage controlled oscillator 172 and the lowpass filter 171 are controlled by the controller 195.
- the voltage controlled oscillator 172 generates the second frequency conection signal depending on the fine frequency offset and provides the generated second frequency conection signal to the frequency conector 161.
- the fine frequency offset is calculated by
- the frequency conector 161 then conects a frequency offset of the received signal according to the first frequency control signal output from the adder 169 and the second frequency conection signal output from the voltage controlled oscillator 172, under the control of the controller 195.
- the frequency synchronizing device is unaffected by the noises generated during OFDM transmission and can acquire frequency synchronization at about 1/2 position of the sub-carrier interval in the frequency domain by performing three steps of coarse, regular and fine frequency synchronization. This secures accurate synchronization and increases the performance of the receiver.
Abstract
A frequency synchronizing device for an OFDM/CDMA communication system which exchanges data using an OFDM frame including OFDM symbols each comprised of a plurality of data samples, and a guard interval inserted at the head of each symbol to prevent interference between the symbols. The frequency synchronizing device comprises a frequency corrector (161) for compensating for a frequency offset of received analog data according to a frequency correction signal; an analog/digital converter (162) for converting the received analog data to OFDM frame; and a frequency synchronizer (200) for detecting copy data which is used for creating the guard interval from the OFDM frame and is comprised of some data samples out of the OFDM symbols, to sequentially estimate coarse, regular and fine frequency offsets, and providing the frequency corrector (161) with the frequency correction signal corresponding to the estimated frequency offsets.
Description
FREQUENCY SYNCHRONIZING DEVICE FOR OFDM/CDMA SYSTEM
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a modulation/demodulation device in an orthogonal frequency division multiplexing/code division multiple access (OFDM/CDMA) system, and in particular, to a device for synchronizing a frequency in a time domain in OFDM/CDMA system.
2. Description of the Related Art In general, an OFDM technique is frequently used in digital transmission systems such as a digital audio broadcasting (DAB) system, a digital television system, a wireless local area network (WLAN), and a wireless asynchronous transfer mode (WATM) system. The OFDM technique is a type of multi-carrier technique which modulates transmission data after dividing, and then transmits the divided modulated data in parallel. The OFDM technique was not widely used for the complex structure. However, the recent progress of various digital signal processing techniques including the fast Fourier transform (FFT) and the inverse FFT (IFFT) has made it possible to utilize the OFDM system. Though similar to the existing FDM system, the OFDM system may have an optimal transmission efficiency during high-speed data transmission by maintaining orthogonality between sub-carriers. Because of the optimal transmission efficiency, the OFDM/TDMA and OFDM/CDMA systems have been proposed for use with the WATM system since it requires high-speed data transmission.
Referring now to FIG. 1, there is shown a block diagram of a general
OFDM/CDMA system. A description will now be made regarding a multi- carrier (MC) CDMA system using the OFDM/CDMA technique. The MC- CDMA system includes a transmitter 100 and a receiver 120. The transmitter 100 and the receiver 120 may be equally applied to both the forward link and the reverse link.
With regard to the transmitter 100, a plurality of spreaders 101 spread transmission data using orthogonal codes of length N and PN spreading sequences. Typically, N is 256 in the OFDM/CDMA system. If the transmitter
100 is a forward transmitter, the spreaders 101 include spreaders for user identification and spreaders for base station identification. On the other hand, if the transmitter 100 is a reverse transmitter, the spreaders 101 include spreaders for channel spreading and spreaders for user identification. Herein, the N-bit data will be referred to as chip data. The chip data spread by the spreaders 101 is input to a summer 102 after pilot signal insertion (not shown). The chip data is summed in the summer 102 on a chip unit basis and is output in series to a serial/parallel converter 103. The serial/parallel converter 103 outputs the serial chip data provided from the summer 102 in parallel. At this point, the number of the parallel chip data output can be equal to N or not equal to N. Herein, the number of the parallel chip data is assumed to be N. Further, the parallel sample data is input to an inverse fast Fourier transform (IFFT) device 104. The IFFT device 104 receiving N parallel data samples, performs OFDM modulation on the chip data. In other words, the IFFT device 104 performs IFFT on the chip data, and carries the processed chip data on different sub-carriers having orthogonality in a frequency domain. In the IFFT device 104, the sub-carriers are output in the time domain. The data output from the IFFT device 104 will be defined as sample data, and N data samples will be defined as an OFDM symbol.
The parallel output sample data is input to a parallel/serial converter 105.
The parallel/serial converter 105 outputs the same data in series. Further, the parallel/serial converter 105 inserts a guard interval on an N-sample data unit basis, i.e., one-OFDM symbol unit basis. The guard interval is data obtained by copying some sample data at the rear of an OFDM symbol comprised of N data samples, and is inserted at the front of the OFDM symbol. Herein, the data in which a guard interval is inserted on an OFDM symbol unit basis, is defined as an OFDM frame. The length of the guard interval should be set longer than an impulse response length. A transmission filter 106 filters the data output from the parallel/serial converter 105 and transmits the filtered data over a radio channel 107 using an RF (Radio Frequency) module (not shown). The radio channel 107 is an additive white Gaussian channel, so that additive white Gaussian noises are added by an adder 109.
The receiver 120 receives a carrier with the additive white Gaussian noises over the additive white Gaussian channel. The received carrier is converted to a baseband signal through an RF module (not shown). A multiplier 110 compensates for frequency error generated in channel 107 using a frequency correction signal received. An analog to digital converter 115 converts the frequency-corrected analog signal input from the multiplier 110 to digital sample
data stream. A serial/parallel converter 111 receives the OFDM symbol in series and outputs N data samples constituting the OFDM symbol in parallel. Though not illustrated, the receiver 120 commonly includes a guard interval remover for removing the guard interval inserted on an OFDM frame unit basis before parallelizing the sample data stream. A fast Fourier transform (FTT) device 112 performs OFDM demodulation on the received sample data carried on the sub- carriers in parallel and converts the respective sub-carriers to the original chip data in the frequency domain. A parallel/serial converter 113 converts the parallel chip data to serial chip data. A despreader 114 despreads the serial chip data input from the parallel/serial converter 113 to restore the original data.
Typically in the OFDM transmission system, if local oscillators in the transmitter and the receiver are not tuned to each other, a frequency offset occurs and causes a loss of orthogonality between the sub-carriers. In this case, even a small frequency offset may cause performance degradation of the receiving system. Therefore, in the OFDM/CDMA WATM transmission system, it is necessary to implement frequency synchronization for maintaining orthogonality between the sub-carriers.
Generally, the frequency synchronization used for a receiver of the
OFDM system is performed in two steps, namely, a coarse synchronization and a fine synchronization. The coarse synchronization step removes an initial frequency offset corresponding to multiples of the sub-carrier interval, and the fine synchronization step removes the residual frequency offset remaining after coarse synchronization.
There are two coarse frequency synchronization techniques; one proposed by Classen & Myer, and another by Nogammi & Nagashima.
FIGS. 2 to 4 show a frequency synchronization device for the receiver, using the coarse frequency synchronization technique and the fine frequency synchronization technique.
First, a description will be made regarding the coarse frequency synchronization technique proposed by Classen & Myer, with reference to FIG. 2.
The technique proposed by Classen & Myer uses a test correction frequency, and calculates a correlation between known transmission data and received data while shifting the test correction frequency by a predetermined
frequency interval, thereby estimating the frequency offset. This technique uses a property that the correlation value becomes maximum when the test correction frequency is nearest to an actual frequency offset shifted in the actual channel.
Referring to FIG. 2, there is shown a block diagram for detecting the test correction frequency offset. A multiplier 128 compensates for a frequency offset of a received signal using a test correction frequency received. An analog/digital converter (ADC) 129 converts the received analog data to digital data. A guard interval remover 122 removes the guard interval from the received data. A guard interval removing method sets a window having a length of two OFDM symbols and one guard interval, calculates a correlation value while shifting the window by samples, and removes the guard interval beginning at a position where the maximum value starts to be output. An FFT device 124 performs FFT to modulate the sample data output from the multiplier 128, and outputs a chip data stream in common to the despreader, a delay 125 and an estimator 127. The delay 125 delays the chip data for one-chip data length time and then outputs the delayed chip data to the estimator 127. A reference tone pattern generator 126 generates a reference tone having a predetermined pattern known to both the mobile station and the base station, and provides the generated reference tone pattern to the estimator 127.
The estimator 127 outputs an estimated frequency offset fe by receiving the chip data output from the FFT device 124, the delayed chip data output from the delay 125 and the reference tone pattern output from the reference tone generator 126. That is, the estimator 127 outputs the estimated frequency offset _ using a correlation value between the chip data of the two consecutive subchannels and the reference tone known to the receiver. The estimated frequency offset fe is a factor in determining the test correction frequency.
The estimator 127 calculates the estimated frequency offset in accordance with Equation ( 1 ) below.
fe = MAX / , ^I+l,k ' T'IJL "*** /+l,*+s ' XlMs (1) k=\
where fe denotes the estimated frequency offset, Zl k and Z]+1 k denote the chip data of the consecutive sub-carriers, Xl k denotes the data stream previously known to the receiver during data reception, V denotes the frequency shift for
sync estimation, '1' denotes an index of the sample data, and 'k' denotes an index of the OFDM symbol. It is noted from Equation (1) that the two consecutive chip data exist in the same OFDM symbol.
Referring to FIG. 3, a description will now be made regarding the coarse frequency synchronization technique proposed by Nogammi & Nagashima. An analog to digital converter (ADC) 131 converts analog data received from a multiplier 140 to digital sample data. A guard interval remover 133 removes from the received data a guard interval which is used for distinguishing the received sample data and for preventing interference between the symbols. An FFT device 135 performs a FFT on the sample data output from the ADC 131, and outputs a chip data stream to both a despreader and a correlator 139. A reference tone pattern generator 137 generates a predetermined reference tone pattern and provides correlator 139 with the reference tone pattern. The conelator 139 outputs an estimated frequency offset fe using the chip data output from the
FFT device 135 and the reference tone pattern output from the reference tone pattern generator 137.
The coarse frequency synchronization technique proposed by Nogammi & Nagashima is different from the technique proposed by Classen & Myer in that a correlation value between one data sample and a reference tone known to the receiver is used for frequency synchronization instead of a correlation value between two consecutive data samples and the reference tone.
The estimated frequency offset according to the technique proposed by
Nogammi & Nagashima is calculated by Equation (2) below.
fe = MAX _ __ (Zι+ι ' Xι,k+s ) (2) k=\
In addition to the coarse frequency synchronization techniques, there are two fine frequency synchronization techniques; one proposed by Dafara & Adami, and another by Moose.
The technique proposed by Dafara & Adami acquires fine frequency synchronization using a property of the transmission signal, namely that when there exists no frequency offset, a signal in the guard interval of the received signal is identical to the original signal. In addition, when there exists a
frequency offset, a signal in the guard interval and the original signal have different phases due to the frequency offset, and finally, when the signal in the guard interval is multiplied by the original signal, an imaginary part of the resulting value contains information about the frequency offset. The present invention removes the residual frequency offset according to this property.
Referring to FIG. 4, a description will now be made regarding the fine frequency synchronization technique. A bandpass filter 141 filters analog data and only permits a frequency band that is proper for the system to pass. A multiplier 143 multiplies the filtered received data by the test correction frequency in order to correct a fine frequency offset. An ADC 145 converts the frequency offset-corrected analog data output from multiplier 143 to digital OFDM frame data. A guard interval remover 153 removes the guard interval included in the OFDM frame from the OFDM frame output from the ADC 145, and outputs OFDM symbols. An FFT device 155 parallelizes the OFDM symbols output from the guard interval remover 153 into N data samples, and performs FFT on the N data samples to output N-chip data.
A frequency detector 147 detects a frequency error for compensating for the fine frequency offset. The frequency detector 147 can detect the frequency error through either a path 'a' or a path 'b'.
The frequency error detection through the path 'a' uses the guard interval.
More specifically, the frequency detector 147 detects the guard interval from the OFDM frame output from the ADC 145. The detected guard interval is compared with a sample data interval in order to detect the frequency error. The sample data interval was used to generate the guard interval out of pure sample data.
Frequency error detection through the path 'b' uses the fast Fourier transformed-chip data from FFT 155. For frequency error detection through the path 'b', a carrier extractor 157 is required. The carrier extractor 157 extracts pilot chip data that is inserted in the chip data stream output from the FFT 155 and provides the frequency detector 147 with the extracted pilot chip data. The frequency detector 147 then detects the frequency error by comparing the pilot chip data with a known signal.
The technique proposed by Dafara & Adami uses the 'a' path wherein the frequency detector 147 uses the guard interval from the digital data output from the ADC 145 and outputs an estimated fine frequency offset calculated by
1 L
(3)
-k k=l where N denotes the sample number of OFDM symbol, and I denotes the sample number in the guard interval.
The technique proposed by Moose uses the 'b' path wherein the frequency detector 147 receives the pilot signal from the FFT device 155 through the carrier extractor 157 and outputs an estimated fine frequency offset calculated by
where L denotes the sample number used when estimating the frequency error.
The estimated fine frequency offset detected by the frequency detector 147 through path 'a' or 'b' is input to a voltage controlled oscillator (VCO) 151 through a lowpass filter 149. The voltage controlled oscillator 151 generates the test correction frequency depending upon the estimated fine frequency offset and provides the generated test correction frequency to the multiplier 143.
The guard interval based (GIB) fine frequency synchronizing technique through the path 'a' is implemented at a pre-FFT stage, and the pilot signal based fine frequency synchronizing technique (or maximum likelihood estimation (MLE)) through the path 'b' is implemented at a post-FFT stage.
If a test correction frequency offset is fe , then the received baseband signal can be expressed as x(t)eJ2πfe' . At this point, in the GIB algorithm, the phase difference between two samples is constantly 2π/ct . However, in the MLE algorithm, the phase difference between two samples is 2πfct' which is affected by the length of the guard interval.
As described above, the conventional coarse frequency synchronization technique is susceptible to channel noises, therefore, it is difficult to guarantee
the system performance.
Further, the fine frequency synchronization is locked at a sub-carrier which is located nearest to a position of the residual frequency offset. However, when the residual frequency offset has a value of about +0.5% of the sub-carrier interval, the conventional fine frequency synchronization technique cannot acquire synchronization.
Moreover, the MLE algorithm processes the data at the post-FFT stage, thereby causing a delay in acquiring synchronization. This delay will increase the time required for synchronization acquisition.
SUMMARY OF THE INVENTION
It is therefore, an object of the present invention to provide a frequency synchronizing device for performing frequency synchronization using only the received input signal in a time domain in an OFDM/CDMA system.
It is another object of the present invention to provide a frequency synchronizing device for acquiring accurate synchronization by performing frequency synchronization in the steps of coarse, regular and fine frequency synchronization in a time domain in an OFDM/CDMA system.
To achieve the above objects, there is provided a frequency synchronizing device for an OFDM/CDMA communication system which exchanges data using an OFDM frame including OFDM symbols each comprised of a plurality of data samples, and a guard interval inserted at the head of each symbol to prevent interference between the symbols. The frequency synchronizing device comprises a frequency corrector for compensating for a frequency offset of the received analog data according to a frequency conection signal; an analog/digital converter for converting the received analog data to an
OFDM frame; and a frequency synchronizer for detecting copy data which is used for creating the guard interval from the OFDM frame. The copy data is comprised of some data samples out of the OFDM symbols and is used to sequentially estimate coarse, regular and fine frequency offsets, and provide the frequency conector with the frequency conection signal conesponding to the estimated frequency offsets.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: FIG. 1 is a block diagram illustrating a general OFDM/CDMA system;
FIG. 2 is a block diagram illustrating a coarse frequency synchronizing device in the general OFDM/CDMA system;
FIG. 3 is a block diagram illustrating another coarse frequency synchronizing device in the general OFDM/CDMA system; FIG. 4 is a block diagram illustrating a fine frequency synchronizing device in the general OFDM/CDMA system; and
FIG. 5 is a block diagram illustrating a frequency synchronizing device for a receiver in an OFDM/CDMA system according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A prefened embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.
Referring to FIG. 5, there is shown a frequency synchronizing device for an OFDM/CDMA system according to an embodiment of the present invention. A bandpass filter 160 filters received analog data. A frequency conector 161 compensates for a frequency offset of the bandpass filtered data according to a first and a second frequency conection signal and a control signal. An ADC 162 converts the received frequency offset-compensated analog data to digital sample data, and provides the digital sample data to a guard interval remover 163. The guard interval remover 163 removes a guard interval which is inserted on a OFDM frame unit basis, from the sample data. A frequency synchronizer 200 calculates an estimated frequency offset for coarse, regular and fine frequency synchronizing depending on a signal output from the ADC 162, and outputs the first and second frequency conection signals according to the estimated frequency offsets.
Now, Reference will be made describing a coarse, regular and fine frequency synchronizing method, respectively.
With regard to the coarse frequency synchronizing method, a controller 195 controls the overall operation of the frequency synchronizing device. In particular, the controller 195 outputs a coarse delay signal for performing initial coarse frequency synchronization, outputs a regular delay signal after acquiring coarse frequency synchronization, and outputs a fine delay signal after acquiring regular frequency synchronization. A delay 164 delays an OFDM frame output from the ADC 162 for a predetermined time. The delay time is identical to one- OFDM frame time. A guard interval/carrier extractor 166 receives the OFDM frame output from the ADC 162 and the OFDM frame output from the delay 164, and extracts therefrom copy data to create the above guard interval and a guard interval in the original OFDM symbol. A shift index generator 165 outputs a shift index of an integer according to the coarse delay signal output from the controller 195, and upon receipt of the regular delay signal, outputs a shift index of 1/10 unit. A coarse frequency synchronizer 180 is comprised of the following: a correlation value detector 167, a minimum/maximum value (MIN/MAX) detector 168, and an adder 169. Conelation value detector 167 receives the guard interval and the copy data from the interval/carrier extractor 166 and the shift index value from the shift index generator 165, and extracts a correlation value while shifting the guard interval and the copy data on a sample data unit basis. The extracted conelation value is provided to a minimum/maximum value (MIN/MAX) detector 168. The MIN/MAX detector 168 detects the maximum or minimum value of the correlation value input from the correlation value detector 166 according to the delay signal output from the controller 195. For coarse frequency synchronization, the MIN/MAX detector 168 detects the minimum value according to the coarse delay signal input from the controller 195. The minimum value detected at this point is a coarse estimation signal. Further, upon detection of the minimum value, the MIN/MAX detector 168 informs the controller 195 of detection of the minimum value.
When there exists a frequency offset, the received signal is shifted overall, so that noises are inserted in the guard interval. By using this property, the coarse frequency offset is estimated in the guard interval/carrier extractor 166, the conelation value detector 167 and the MIN/MAX detector 168. The estimated frequency offset for coarse frequency synchronization by detecting guard interval power in the time domain is calculated by
where i denotes the size of a sliding window, KMIN and KMAX denote the minimum and maximum sub-carrier numbers of FFT, respectively, and Zi denotes a symbol.
Second, with regard to the regular frequency synchronizing method, the guard interval/carrier extractor 166 extracts the guard interval and copy data from an OFDM frame output from the ADC 162. The conelation value detector 167 receives the guard interval and copy data from the guard interval/carrier extractor 166 and a shift index having 1/10 length of the sample data from the shift index generator 165, and detects a conelation value while shifting the sample data in the detected guard interval and sample data of the copy data, which is identical to the above sample data, by 1/10 band. The MIN/MAX detector 168 detects a conelation value having the maximum power out of the conelation values detected by the conelation value detector 167, and outputs a regular estimated frequency offset which is a regular estimation signal. The estimated frequency offset for regular frequency synchronization is calculated by
. =MAX\ ∑(Z;+U -Z k) XliMs -XlMs (6)
where f^a, denotes a compulsory test conection frequency and has a value larger than '0' but smaller than '1 '. Once the compulsory test conection frequency interval is selected, the regular frequency offset is determined while increasing it at the unit interval. In Equation (6), Z denotes sample data in the guard interval, and X denotes the copy data.
After estimation of the coarse frequency offset and the regular frequency offset, the MIN/MAX detector 168 outputs the coarse estimation signal and a regular estimation signal. An adder 169 adds the coarse estimation signal to the regular estimation signal to generate the first frequency correction signal, and provides the first frequency conection signal to the frequency conector 161.
With regard to the fine frequency synchronizing method, the guard interval/carrier extractor 166 extracts the guard interval and copy data from an OFDM frame output from the ADC 162, and provides the extracted guard interval and copy data to a frequency detector 170. The fine frequency synchronization is accomplished using a fine frequency synchronizer 190 and is
performed after acquiring the coarse and regular frequency synchronization. Fine frequency synchronizer 190 is comprised of frequency detector 170, a lowpass filter 171and a voltage controlled oscillator (NCO). The GIB frequency synchronization technique described with reference to FIG. 4 is used for the fine frequency synchronization. That is, frequency detector 170, under the control of controller 195, receives the sample data in the guard interval output from the guard interval/carrier extractor 166 and sample data of the copy data, which is identical to the above sample data, to detect a phase difference between the two sample data, and determines the detected phase difference as a fine frequency offset. The frequency detector 170 provides the fine frequency offset to a voltage controlled oscillator (VCO) 172 via a lowpass filter 171. The voltage controlled oscillator 172 and the lowpass filter 171 are controlled by the controller 195. The voltage controlled oscillator 172 generates the second frequency conection signal depending on the fine frequency offset and provides the generated second frequency conection signal to the frequency conector 161. The fine frequency offset is calculated by
The frequency conector 161 then conects a frequency offset of the received signal according to the first frequency control signal output from the adder 169 and the second frequency conection signal output from the voltage controlled oscillator 172, under the control of the controller 195.
The frequency synchronizing device according to the present invention is unaffected by the noises generated during OFDM transmission and can acquire frequency synchronization at about 1/2 position of the sub-carrier interval in the frequency domain by performing three steps of coarse, regular and fine frequency synchronization. This secures accurate synchronization and increases the performance of the receiver.
While the present invention has been shown and described with reference to a certain prefened embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made thereunto without departing from the spirit and scope of the invention as defined by the appended claims.
Claims
1. A frequency synchronizing device for an OFDM/CDMA (Orthogonal Frequency Division Multiplexing/Code Division Multiple Access) communication system which exchanges data using an OFDM frame including OFDM symbols each comprised of a plurality of data samples, and a guard interval inserted at the head of each symbol to prevent interference between the symbols, the frequency synchronizing device comprising: a frequency conector for compensating for a frequency offset of received analog data according to a frequency conection signal; an analog/digital converter for converting the received analog data to the OFDM frame; and a frequency synchronizer for sequentially estimating a coarse, a regular and a fine frequency offset, and for providing said frequency corrector with said frequency conection signal conesponding to said estimated coarse, regular and fine frequency offsets.
2. The frequency synchronizing device according to claim 1, further comprising a controller for generating a control signal for sequentially performing coarse, regular and fine frequency synchronization.
3. The frequency synchronizing device according to claim 2, wherein said frequency synchronizer comprises: a guard interval/carrier extractor for extracting the guard interval and copy data from the OFDM frame; a shift index generator for generating a shift index of integer or 1/10 decimal according to the control signal; a coarse frequency synchronizer for receiving first sample data in the guard interval and second sample data of copy data, and detecting a correlation value between the first and second sample data while shifting the first and second sample data according to the shift index, to output a first frequency correction signal to the frequency corrector; and a fine frequency synchronizer for performing a phase-locked loop on the first and second sample data provided after coarse frequency synchronization, to output a second frequency conection signal to the frequency conector.
4. The frequency synchronizing device as claimed in claim 3, wherein said coarse frequency synchronizer comprises: a conelation value detector for detecting a conelation value while shifting the first and second sample data according to the shift index; a maximum/minimum value detector for detecting a minimum value out of the conelation values to output a coarse estimation signal when the control signal is a coarse control signal, and detecting a maximum value out of the conelation values to output a regular estimation signal when the control signal is a regular control signal; and an adder for adding the coarse estimation signal to the regular estimation signal to output the first frequency conection signal to the frequency conector.
5. The frequency synchronizing device as claimed in claim 4, wherein the coarse estimation signal is calculated by
6. The frequency synchronizing device as claimed in claim 4, wherein the regular estimation signal is calculated by
7. The frequency synchronizing device as claimed in claim 3, wherein the fine frequency synchronizer further comprises: a frequency detector for detecting a pilot signal of a carrier output from the guard interval/carrier extractor; a lowpass filter for filtering the pilot signal detected by the frequency detector; and a voltage controlled oscillator for outputting a second frequency conection signal depending on the pilot signal output from the lowpass filter, to conect the fine frequency offset.
8. The frequency synchronizing device as claimed in claim 7, wherein the second frequency conection signal is a fine estimation offset signal.
Priority Applications (3)
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JP2000586030A JP3428965B2 (en) | 1998-12-01 | 1999-12-01 | Frequency synchronizer for orthogonal frequency division multiplexing / code division multiple access system |
EP99958501A EP1051818B1 (en) | 1998-12-01 | 1999-12-01 | Frequency synchronizing device for ofdm/cdma system |
DE69939310T DE69939310D1 (en) | 1998-12-01 | 1999-12-01 | DEVICE FOR FREQUENCY SYNCHRONIZATION OF AN OFDM / CDMA SYSTEM |
Applications Claiming Priority (2)
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KR19980052234 | 1998-12-01 | ||
KR1998/52234 | 1998-12-01 |
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PCT/KR1999/000726 WO2000033496A1 (en) | 1998-12-01 | 1999-12-01 | Frequency synchronizing device for ofdm/cdma system |
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US (1) | US6373861B1 (en) |
EP (1) | EP1051818B1 (en) |
JP (1) | JP3428965B2 (en) |
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WO (1) | WO2000033496A1 (en) |
Cited By (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1195961A2 (en) * | 2000-09-29 | 2002-04-10 | Samsung Electronics Co., Ltd. | Frequency offset correction in multicarrier receivers |
FR2823395A1 (en) * | 2001-04-05 | 2002-10-11 | Canon Kk | OFDM modulated signals receiver synchronisation mechanism has signals sampled/reference determined and separation operation/transformation carried out and correction operation affected. |
WO2006099532A2 (en) * | 2005-03-11 | 2006-09-21 | Qualcomm Incorporated | Automatic frequency control for a wireless communication system with multiple subcarriers |
WO2007052981A2 (en) * | 2005-11-04 | 2007-05-10 | Lg Electronics Inc. | Method of transmitting signals for initial synchronization in a wireless communication system using orthogonal frequency division multiplexing (ofdm) or ofdm access (ofdma) scheme |
CN100346591C (en) * | 2001-02-27 | 2007-10-31 | 美商内数位科技公司 | Initial cell search algorithm |
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WO2010103395A1 (en) * | 2009-03-13 | 2010-09-16 | Advanced Micro Devices, Inc. | Synchronization and acquisition for mobile television reception |
US8401503B2 (en) | 2005-03-01 | 2013-03-19 | Qualcomm Incorporated | Dual-loop automatic frequency control for wireless communication |
WO2014069953A1 (en) * | 2012-11-04 | 2014-05-08 | 엘지전자 주식회사 | Synchronizing signal receiving method and user equipment, and synchronizing signal transmitting method and base station |
Families Citing this family (61)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6876675B1 (en) * | 1998-02-06 | 2005-04-05 | Cisco Technology, Inc. | Synchronization in OFDM systems |
EP1061746A1 (en) * | 1999-06-14 | 2000-12-20 | Sony International (Europe) GmbH | Channel decoder for a digital broadcast receiver |
US6862297B1 (en) * | 1999-12-21 | 2005-03-01 | Cisco Technology, Inc. | Wide range frequency offset estimation in OFDM systems |
JP2001320342A (en) * | 2000-05-11 | 2001-11-16 | Nec Corp | Fdm-cdma transmitting method, fdm-cdma receiving method and device for these |
FI20001289A (en) * | 2000-05-30 | 2001-12-01 | Nokia Mobile Phones Ltd | Method and arrangement for reducing frequency offset in a radio receiver |
US6930989B1 (en) | 2000-06-20 | 2005-08-16 | Cisco Technology, Inc. | Wide frequency offset correction using encoded interburst phase differences |
IT1318161B1 (en) * | 2000-07-14 | 2003-07-23 | Cit Alcatel | METHOD AND DEVICE FOR THE RECOVERY OF CARRIER IN OFDM SYSTEMS |
GB2369015A (en) * | 2000-11-09 | 2002-05-15 | Sony Uk Ltd | Receiver that uses guard signals to estimate synchronisation position |
FR2816776B1 (en) * | 2000-11-10 | 2003-02-07 | Cit Alcatel | METHOD FOR CORRECTING THE FREQUENCY ERROR |
US7106709B2 (en) * | 2000-11-29 | 2006-09-12 | Telefonaktiebologet Lm Ericsson (Publ) | Timing drift compensation in wireless packet-based systems |
JP4341176B2 (en) * | 2000-12-08 | 2009-10-07 | ソニー株式会社 | Reception synchronizer and demodulator using the same |
US7012881B2 (en) * | 2000-12-29 | 2006-03-14 | Samsung Electronic Co., Ltd. | Timing and frequency offset estimation scheme for OFDM systems by using an analytic tone |
US7218666B2 (en) * | 2000-12-29 | 2007-05-15 | Motorola, Inc. | Method and system for transmission and frequency domain equalization for wideband CDMA system |
GB0104280D0 (en) * | 2001-02-21 | 2001-11-21 | Cambridge Silicon Radio Ltd | Estimating frequency offset |
US7248652B2 (en) * | 2001-02-28 | 2007-07-24 | Agere Systems Inc. | Method and apparatus for recovering timing information in orthogonal frequency division multiplexing (OFDM) systems |
US6940827B2 (en) | 2001-03-09 | 2005-09-06 | Adaptix, Inc. | Communication system using OFDM for one direction and DSSS for another direction |
US7035201B2 (en) * | 2001-04-20 | 2006-04-25 | Mediatek Inc. | Programmable transceiver structure of multi-rate OFDM-CDMA for wireless multimedia communications |
US7088782B2 (en) * | 2001-04-24 | 2006-08-08 | Georgia Tech Research Corporation | Time and frequency synchronization in multi-input, multi-output (MIMO) systems |
US7310304B2 (en) * | 2001-04-24 | 2007-12-18 | Bae Systems Information And Electronic Systems Integration Inc. | Estimating channel parameters in multi-input, multi-output (MIMO) systems |
US7706458B2 (en) * | 2001-04-24 | 2010-04-27 | Mody Apurva N | Time and frequency synchronization in Multi-Input, Multi-Output (MIMO) systems |
JP3628977B2 (en) * | 2001-05-16 | 2005-03-16 | 松下電器産業株式会社 | Radio base station apparatus and communication terminal apparatus |
EP1267536A1 (en) * | 2001-06-13 | 2002-12-18 | Conexant Systems, Inc. | Multicarrier receiver with detection of the transmission mode and length of the guard interval |
US7027534B2 (en) * | 2001-06-22 | 2006-04-11 | Sirf Technology, Inc. | Extracting fine-tuned estimates from correlation functions evaluated at a limited number of values |
US7826493B2 (en) * | 2001-08-27 | 2010-11-02 | Broadcom Corp. | Frequency offset correction circuit for WCDMA |
US7430191B2 (en) * | 2001-09-10 | 2008-09-30 | Qualcomm Incorporated | Method and apparatus for performing frequency tracking based on diversity transmitted pilots in a CDMA communication system |
WO2003032542A1 (en) * | 2001-09-28 | 2003-04-17 | Fujitsu Limited | Frequency synchronizing method, and frequency synchronizing device |
CA2428576C (en) * | 2002-05-16 | 2008-10-07 | Ntt Docomo, Inc. | Transmitter for multi-carrier transmission and multi-carrier transmitting method |
US20050276311A1 (en) * | 2002-06-25 | 2005-12-15 | Koninklijke Philips Electronics N.V. | Mt-cdma using spreading codes with interference-free windows |
SG129231A1 (en) * | 2002-07-03 | 2007-02-26 | Oki Techno Ct Singapore Pte | Receiver and method for wlan burst type signals |
CN100579309C (en) * | 2002-08-23 | 2010-01-06 | 松下电器产业株式会社 | OFDM-CDMA transmission device and OFDM-CDMA transmission method |
US7280464B1 (en) * | 2002-09-27 | 2007-10-09 | Rockwell Collins, Inc. | Featureless synchronization in multi-user OFDM |
US7889819B2 (en) * | 2002-10-04 | 2011-02-15 | Apurva Mody | Methods and systems for sampling frequency offset detection, correction and control for MIMO OFDM systems |
KR100470401B1 (en) * | 2002-12-24 | 2005-02-05 | 한국전자통신연구원 | A wireless communication system and method using grouping Maximum Lilelihood Detection |
US7684501B2 (en) * | 2003-02-19 | 2010-03-23 | Realtek Semiconductor Corp. | Apparatus and method for carrier frequency offset and phase compensation in communication system |
KR100528332B1 (en) * | 2003-03-15 | 2006-01-09 | 삼성전자주식회사 | Coarse frequency synchronization method and apparatus in OFDM system |
TWI252656B (en) * | 2003-03-21 | 2006-04-01 | Realtek Semiconductor Corp | Sampling clock compensation device of multi-carrier system and method thereof |
SE527445C2 (en) | 2003-03-25 | 2006-03-07 | Telia Ab | Position-adjusted protection interval for OFDM communication |
US7224754B2 (en) * | 2003-06-02 | 2007-05-29 | Silicon Integrated Systems Corp. | Frequency offset compensation estimation system and method for a wireless local area network |
TWI220547B (en) * | 2003-07-08 | 2004-08-21 | Realtek Semiconductor Corp | Symbol boundary detection device and method |
US7277457B2 (en) * | 2003-10-03 | 2007-10-02 | Motorola, Inc. | Sync bursts for frequency offset compensation |
KR100590354B1 (en) * | 2003-12-15 | 2006-06-15 | 삼성탈레스 주식회사 | An Apparatus and Method for compensation for residual frequency offset in OFDM system |
KR100601939B1 (en) * | 2004-01-16 | 2006-07-14 | 삼성전자주식회사 | Coarse frequency synchronization method and apparatus in OFDM system |
US7515657B1 (en) * | 2004-03-05 | 2009-04-07 | Marvell International Ltd. | Frequency tracking for OFDM transmission over frequency selective channels |
JP4583374B2 (en) * | 2004-04-14 | 2010-11-17 | パナソニック株式会社 | Receiver |
US7336732B1 (en) * | 2004-07-28 | 2008-02-26 | L-3 Communications Titan Corporation | Carrier frequency detection for signal acquisition |
US7272756B2 (en) * | 2005-05-03 | 2007-09-18 | Agere Systems Inc. | Exploitive test pattern apparatus and method |
US7447965B2 (en) * | 2005-05-03 | 2008-11-04 | Agere Systems Inc. | Offset test pattern apparatus and method |
JP4775703B2 (en) * | 2005-10-05 | 2011-09-21 | カシオ計算機株式会社 | Wireless television system, wireless television receiver and transmitter |
JP2007181016A (en) * | 2005-12-28 | 2007-07-12 | Oki Electric Ind Co Ltd | Determination timing synchronizing circuit and reception circuit |
KR20070095135A (en) * | 2006-03-20 | 2007-09-28 | 삼성전자주식회사 | Apparatus and control method of inter subcarrier interface suppresion in wireless ofdma system |
KR20070095138A (en) | 2006-03-20 | 2007-09-28 | 삼성전자주식회사 | Up link signal receiving apparatus and method of multiuser detection using successive interference cancellation in wireless ofdma system |
TW200913592A (en) * | 2007-05-25 | 2009-03-16 | Amicus Wireless Technology Ltd | OFDM-based device and method for performing synchronization in the presence of interference signals |
US7978749B2 (en) * | 2007-07-13 | 2011-07-12 | Crestcom, Inc. | Bandjamming multi-channel DSSS transmitter and method therefor |
US8351519B2 (en) * | 2008-08-15 | 2013-01-08 | Qualcomm Incorporated | Embedding information in an 802.11 signal field |
US20100046656A1 (en) * | 2008-08-20 | 2010-02-25 | Qualcomm Incorporated | Preamble extensions |
US20100290449A1 (en) | 2008-08-20 | 2010-11-18 | Qualcomm Incorporated | Preamble extensions |
KR101038855B1 (en) * | 2008-12-04 | 2011-06-02 | 성균관대학교산학협력단 | Frequency synchronization apparatus in ofdm system |
US8576743B2 (en) * | 2010-12-28 | 2013-11-05 | Qualcomm Incorporated | Apparatus and methods for estimating an unknown frequency error of a tone signal |
TW201611553A (en) * | 2014-09-09 | 2016-03-16 | 聯詠科技股份有限公司 | Device and method for detecting guard interval of orthogonal frequency division multiplexing signal |
EP3387754B1 (en) * | 2015-12-07 | 2021-05-12 | Telefonaktiebolaget LM Ericsson (publ) | Wireless communication device and method therein for time synchronization in a wireless communication network |
KR101935991B1 (en) * | 2017-02-14 | 2019-01-07 | 국방과학연구소 | Extreme fine frequency estimation apparatus and method of single receiver |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5444697A (en) * | 1993-08-11 | 1995-08-22 | The University Of British Columbia | Method and apparatus for frame synchronization in mobile OFDM data communication |
EP0851641A2 (en) * | 1996-12-26 | 1998-07-01 | Sony Corporation | Communication method and receiving apparatus for OFDM systems |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP3041175B2 (en) * | 1993-11-12 | 2000-05-15 | 株式会社東芝 | OFDM synchronous demodulation circuit |
US5953311A (en) * | 1997-02-18 | 1999-09-14 | Discovision Associates | Timing synchronization in a receiver employing orthogonal frequency division multiplexing |
US6130922A (en) * | 1997-05-02 | 2000-10-10 | Lsi Logic Corporation | Demodulating digital video broadcast signals |
US6134286A (en) * | 1997-10-14 | 2000-10-17 | Ericsson Inc. | Synchronization techniques and systems for radiocommunication |
EP1028564B1 (en) * | 1999-02-11 | 2010-04-07 | Motorola, Inc. | Estimation of carrier and sampling frequency offsets in multicarrier receivers |
-
1999
- 1999-12-01 DE DE69939310T patent/DE69939310D1/en not_active Expired - Lifetime
- 1999-12-01 JP JP2000586030A patent/JP3428965B2/en not_active Expired - Fee Related
- 1999-12-01 WO PCT/KR1999/000726 patent/WO2000033496A1/en active Application Filing
- 1999-12-01 EP EP99958501A patent/EP1051818B1/en not_active Expired - Lifetime
- 1999-12-01 US US09/452,359 patent/US6373861B1/en not_active Expired - Fee Related
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5444697A (en) * | 1993-08-11 | 1995-08-22 | The University Of British Columbia | Method and apparatus for frame synchronization in mobile OFDM data communication |
EP0851641A2 (en) * | 1996-12-26 | 1998-07-01 | Sony Corporation | Communication method and receiving apparatus for OFDM systems |
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Also Published As
Publication number | Publication date |
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DE69939310D1 (en) | 2008-09-25 |
JP3428965B2 (en) | 2003-07-22 |
EP1051818B1 (en) | 2008-08-13 |
JP2002531999A (en) | 2002-09-24 |
US6373861B1 (en) | 2002-04-16 |
EP1051818A1 (en) | 2000-11-15 |
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